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APPKNDIX                                   295
method for determining the number of mctlioxyl groups (OCH-.j
present in a compound iZcisel, see p. 220).
Hexahydrophenol—llic method of Sabatier and Sen-
derens for the reduction of organic compounds is very generally
applicable. It consists in passing the vapour of the organic
compound mixed with - hydrogen over finely divided metals,
especially nickel, as in the example given. Aldehydes and
Uotoni's arc. reduced to alcohols*, olefincs to paraffins, and, in
the aromatic series, hydrogen is taken up in the nucleus and
hydrocyclic compounds result. The hydrocarbons form cyclo-
paraflms ; the phenols, cyclic alcohols ; the bases, cyclic
amines, &c.
o- and p-Nitrophenol. The action of nitric acid on
phenol is much more energetic than it is in the case of
hen/em.'. To obtain the. mono-derivatives, the acid has, in
consequence, to be diluted.
The entrance of the nilro-group renders the phenol more
strongly acid, so that the nitrophenols, unlike the phenols, form
stable salts with alkaline; carbonates. It should be noted that
the nitro-groiip enters the ortho- and para-position, but not the
meta-position to the Oil group, according to the general rule
explained on p. 274. Moreover, the ortho-compound is more
volatile than the para-compound. Compare o- and />-hydr-
oxybcn/.aldehyde (Prep. Sj, p. i 88).
Picric Acid.......The presence of three nilro-groiips converts
the phenol into a strong acid. Picryl chloride, which is formed
by the action of PC1-, on the acid, behaves like an acid chloride,
is decomposed by water and alkalis and forms picramide or
trinilraniline with ammonia,
<',jll.,(N0,);!n  I  N1IS r- c:(i!I,(NO,):,Nn,, -1- IIC1.
Note that the throe nitro-groups occupy meta-positions in
regard to one another ; ortho- or para-positions in reference
to t4ic hvdroxvl group.